The present invention generally relates to a method and an appliance for cooling a shaft region at an inlet flow to a steam turbine.
DE 198 23 251 C1, from the same applicant describes a method and an appliance for cooling a shaft region at the inlet flow to a low-pressure stage of a steam turbine. This publication proposes the injection of a cooling medium, in particular condensate or steam from a cooling system, into the low-pressure stage as a function of the relationships in the low-pressure stage.
A disadvantageous feature of this known procedure is that the injection of the cooling medium and the supply of the live steam have to be controlled separately and independently of one another. For this reason, quick-acting stop valves are necessary for both the cooling medium and the live steam. These valves must be triggered substantially simultaneously and must close substantially simultaneously in order to ensure the necessary protection against excess rotational speed and excessively high condenser pressure. The result is a complicated design and control system.
An object of an embodiment of the present invention includes, therefore, to make available a simple method for cooling the shaft region at the inlet flow to a steam turbine. In addition, an appliance may be, in one embodiment, made available for cooling the shaft region at the inlet flow location, which appliance has a simple structural design.
A concept of an embodiment of the invention provides for the live steam flow supplied to the steam turbine to be divided. A partial mass flow is branched off, cooled and returned, whereas the residual mass flow is supplied directly. In order to realize the method according to an embodiment of the invention, particular provision is made for a partial mass flow to be branched off upstream of a supply system for steam to the steam turbine, cooled and subsequently conducted to the supply system and from the latter, together with the residual mass flow, into the steam turbine. The device according to an embodiment of the invention provides for the live steam main to have a branch for extracting a partial mass flow to be cooled, which branch returns to the supply system downstream of a cooling device for the partial mass flow.
In consequence, it is now only necessary to provide one quick-acting stop valve, which is arranged upstream of the branch. It is therefore possible to dispense with a further quick-acting stop valve for an injected cooling medium. The structural design and the control system are substantially simplified.
In an advantageous embodiment, the partial mass flow branched off is less than 10% of the mass flow supplied and is, in particular, located between 5% and 7% of the mass flow supplied. This avoids branching off an unallowably high partial mass flow and, therefore, avoids a reduction in the power of the steam turbine.
A fluid extracted from a principal feed main is advantageously used for cooling the partial mass flow. The fluid is extracted upstream of a steam generator or a reheater. An additional supply main is unnecessary.
In an advantageous first development, the partial mass flow is cooled in a heat exchanger. The fluid extracted from a principal feed main is conducted through the heat exchanger and heated in the process. It is then advantageously returned to the principal supply main upstream of the steam generator or the reheater. There are therefore no heat losses.
According to an advantageous second development, the partial mass flow is cooled by injecting a flow of water. In this arrangement, the temperature of the partial mass flow is generally so high that the flow of water injected is completely evaporated and then conducted, together with the partial mass flow branched off, to the supply system and from the latter into the steam turbine. Here again, therefore, there are no heat losses.
According to an advantageous embodiment, the temperature of the cooled partial mass flow is measured downstream of the cooling location. The temperature of the partial mass flow can therefore be set in a targeted manner to a predefined required value so that an open-chain or closed-loop control of the temperature is also possible. The required value is advantageously fixed as a function of the conditions in the steam turbine to be cooled.
In an advantageous development, the cooled partial mass flow and the residual mass flow are fed into the steam turbine separately from one another. The partial mass flow can then be conducted in a targeted manner to those locations at which cooling is necessary. The residual mass flow can, on the other hand, be conducted directly to the steam turbine blading.
In the appliance according to an embodiment of the invention, the branch leads from the live steam feed to a heat exchanger, which is cooled by a fluid extracted from the principal feed main. As an alternative, the branch can lead to a cooling chamber, into which water extracted from a principal feed main can be injected. A further supply conduit is unnecessary. In addition, the heat extracted from the partial mass flow remains in the system.
A temperature sensor for measuring the temperature of the cooled partial mass flow is advantageously arranged downstream of the cooling location. In this way, the partial mass flow can be cooled in a targeted manner to a specified temperature, which is in turn specified as a function of the conditions in the steam turbine. In this arrangement, the temperature sensor can be part of a temperature closed-loop circuit or a temperature control device.
In an advantageous embodiment, the heat exchanger or the cooling chamber is provided with a drainage system. The drainage system permits the removal of condensate and, therefore, disturbance-free uninterrupted operation.
According to an advantageous development, the supply system has a nozzle for the residual mass flow and a further nozzle for the cooled partial mass flow. Any mixing of the two mass flows is avoided. The cooled partial mass flow can therefore be conducted in a targeted manner into the shaft region (which has to be cooled) at the inlet flow location, whereas the residual mass flow can be deflected directly onto the steam turbine blading.